A study of resonance tongues near a Chenciner bifurcation using MatcontM

MatcontM is a matlab toolbox for numerical analysis of bifurcations of fixed points and periodic orbits of maps. It computes codim 1 bifurcation curves and supports the computation of normal coefficients including branch switching from codim 2 points to secondary curves. Recently, the initialization and computation of connecting orbits was improved. Moreover, a graphical user interface was added enabling interactive control of all these computations. To further support these computations it allows to compute orbits of the map and its iterates and to represent them in 2D, 3D and numeric windows. We demonstrate the use of the toolbox in a study of Arnol'd tongues near a degenerate Neimark-Sacker (Chenciner) bifurcation. Here we illustrate the recent theory of [Baesens&Mackay,2007] how resonance tongues interact with a quasi-periodic saddle-node bifurcation of invariant curves in maps. Using normal form coefficients we find evidence for one of their cases, but not the other. Actually, we find another unfolding, i.e. a third possibility. We also find a structure that resembles a quasi-periodic cusp bifurcation of invariant curves

Impact of ingredient interactions on the physico-chemical stability of milk protein-stabilised oil-in-water emulsions

Besides an oil phase and an aqueous phase, emulsions also contain an emulsifier (e.g. protein). In addition, most food emulsions contain other ingredients, which are intended to adjust the macroscopic appearance, rheology or gravitational stability. Thickeners are used to slow down creaming or sedimentation phenomena. Using a model system including guar gum in a sodium caseinate stabilised oil-in-water emulsion, it was shown that intermediate concentrations may have the opposite effect: in fact, faster creaming may occur due to depletion flocculation effects when adding a neutral polysaccharide to these protein-stabilised emulsions. This macroscopic demixing could be reduced by formation of a sufficiently strong three-dimensional network, which could be realised by further increasing the guar gum concentration and/or the ionic strength. Hence, the macroscopic behaviour is dependent on a complex interplay of electrostatic and depletion interactions on the one hand, and bulk viscosity effects on the other hand. Anionic polysaccharides, such as pectins, were used to improve the stability of protein-stabilised emulsions around the protein’s iso-electric point by adsorption onto the interfacial protein layer, resulting in a beneficial combination of electrostatic and steric effects. However, rather large amounts of pectin were required since electrostatic interactions are weak around the iso-electric point. Our experiments revealed that covalent coupling of polysaccharides to proteins by mild heat treatment of dry mixtures is a promising technique to largely improve the emulsion stability around the protein’s iso-electric point. In this particular case, the surface-active protein transports the bound highly charged and hydrophilic polysaccharide towards the O/W interface and hence gives rise to a pronounced electrosteric stabilisation. As a last example, heat-induced coagulation in a coffee cream simulant has been studied. Heat coagulation may lead to an excessive increase of the viscosity of sterilised concentrated milk. It was observed that hydrolysed lecithin led to a heat-stabilising effect. Addition of such lecithin significantly reduced the additional protein adsorption upon sterilisation. It is suggested that the heat-stabilising effect of lecithin is due to the fact that it largely reduces attractive protein-protein interactions, such as interactions between whey proteins or between (aggregated) whey proteins and casein micelles, upon severe heating

Urban foraging : target and location choice among graffiti writers

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Combining scripting and commercial simulation software to simulate in-plant logistics

In this paper we describe the use of a commercial discrete event simulation package (Siemens 2008) combined with a custom program, written in the programming language Python (Martelli 2006). Combining these two makes it possible to automatically generate a model for assembly line logistics simulation. The different stations of the assembly line, their connections and the storage near the assembly line were generated within seconds. A huge amount of time was saved compared with manual generation